1) to be able, have power whether by virtue of one's own ability and resources, or of a state of mind, or through favourable circumstances, or by permission of law or custom
2) to be able to do something
3) to be capable, strong and powerful
Part of Speech: verb
Citing in TDNT: 2:284, 186
Of uncertain affinity; to be able or possible: - be able, can (do, + -not), could, may, might, be possible, be of power.
These two sites give similar information, with the definition from several dictionaries and statistics on the use of the word.
Perseus Digital Library
University of Chicago's Logion lexicon
Thayer's dictionary plus other information.
From this site's dictionary (in Italian)
Click on the first column to search for that word as a form of the root δύναμαι; click on the second column to search for that grammatical form of the root δύναμαι; click on the third column to search for that word and grammatical form; click on the total to search for the root δύναμαι.